Electrochemical batteries, including, for example, lead acid and nickel-based batteries, among others, are known to include at least one positive current collector, at least one negative current collector, and an electrolytic solution. In lead acid batteries, for example, both the positive and negative current collectors are constructed from lead. The role of these lead current collectors is to transfer electric current to and from the battery terminals during the discharge and charging processes. Storage and release of electrical energy in lead acid batteries is enabled by chemical reactions that occur in a chemically active material disposed on the current collectors. The positive and negative current collectors, once coated with this chemically active material, are referred to as positive and negative plates, respectively. A notable limitation on the durability of lead-acid batteries is corrosion of the current collectors and other components of the battery.
One method of extending the service life of a lead acid battery is to increase the corrosion resistance of the components included in the battery. Several methods have been proposed for inhibiting the corrosion process in lead acid batteries. Because carbon does not oxidize at the temperatures at which lead-acid batteries generally operate, some of these methods have involved using carbon in various forms to slow or prevent the detrimental corrosion process in lead acid batteries. For example, U.S. Pat. No. 5,512,390 (hereinafter the '390 patent) discloses a lead acid battery that includes current collectors made from graphite plates instead of lead. The graphite plates have sufficient conductivity to function as current collectors, and they are more corrosion resistant than lead. Substituting graphite plates for the lead current collectors may, therefore, lengthen the life of a lead-acid battery.
While the battery of the '390 patent may potentially offer a lengthened service life as a result of reduced corrosion, the graphite plates of the '390 patent are problematic. For example, the graphite plates of the '390 patent are dense, flat sheets of material each having a relatively small amount of surface area. Unlike lead electrode plates of a conventional lead-acid battery, which are generally patterned into a grid-like structure to increase the available surface area of the plates, the graphite plates of the '390 patent are smooth sheets with no patterning. In lead acid batteries, an increase in surface area of the current collector may increase the specific energy and power of the battery and, therefore, may translate into improved battery performance. More surface area on the current collectors may also lead to a reduction in the time required for charging and discharging of the battery. The relatively small surface area of the graphite plates of the '390 patent may result in poorly performing batteries that have slow charging times.
Additionally, the graphite plates of the '390 patent lack the toughness of lead current collectors. The dense, graphite plates of the '390 patent can be brittle and may fracture when subjected to physical shock or vibration. Such physical shock and vibration commonly occur in vehicular applications, for example. Any fracturing of the graphite plates would lead to degradation of the current carrying ability of the graphite plates. Therefore, despite offering an increased resistance to corrosion, the brittle nature of the graphite plates of the '390 patent could actually result in battery service lives shorter than those possible through use of ordinary non-carbon based materials.
The present invention is directed to overcoming one or more of the problems or disadvantages existing in the prior art.